This invention relates to a charged particle apparatus including synchrotrons and storage rings for accelerating charged particle beams such as electron beams.
The charged particle apparatus according to the present invention can be applied to both synchrotrons and storage rings. The following description will be given taking a storage ring into consideration, and electron beams are chosen as an example for the representative charged particle beams.
In a conventional storage ring plural pairs of quadrupole electromagnets for focusing electrons, plural bending electromagnets for deflecting the electrons, bump electromagnets for generating a fast-pulse magnetic field and radio frequency cavities for generating a radio frequency electric field are disposed along an equilibrium orbit which passes through inflectors located at the electron injection site. The storage ring thus constructed causes an electron beam of high energy to run along the equilibrium orbit and enables the high-energy electron beam to maintain its kinetic energy for several hours to several tens of hours.
One of the applications of the storage ring is a light source for manufacturing very large scale integrated circuits (VLSIs) in which synchrotron radiation is utilized. It is injected when the high-energy electron beam is running along the equilibrium orbit. Conventionally, a linear accelerator or a synchrotron of the known kind is provided on the upstream side of the storage ring.
The electron beam is fed from the accelerator through inflectors disposed in part of the straight sections of the storage ring. These straight sections are free from any magnetic fields or electric fields, and in which the inflectors, bump electromagnets and radio frequency cavities having the following functions are disposed. The electron beam of high energy circulating in the storage ring runs along the equilibrium orbit having a weak focusing magnetic field distribution.
The electron beam injected from the accelerator into the storage ring has a fixed angle with respect to the straight section of the orbit. The electron beam passing through the inflector having its center of curvature located directly opposite to that of the bending electromagnets runs parallel with the orbit and is then injected from the inflector into the storage ring. As is well known, the deflection of the electron beam is performed by an electric field produced between the negative and positive electrodes of the inflector, whose center of curvature is located opposite to that of the storage ring. Although the electron beam injected from the inflector runs parallel with the equilibrium orbit, its center has a certain amount of deviation from the center of the orbit; the sectional center of the electron beam thus oscillates around the equilibrium orbit and collides with a vacuum tank containing the electron beam to cause the partial loss of the beam.
The amplitude of the oscillation is equal to the deviation of the electron beam. Because of this the electron beam, after passing through the inflector, tends to have a reduced central amplitude and intersects with the orbit. If the angle between the electron beam and the orbit at this first intersection made after the injection can be made zero, the loss in the electron beam can be minimized.
The bump electromagnet is disposed at this intersection to achieve this purpose. The time requirement of its high speed pulse magnetic field is determined by the speed at which the magnetic field of the bump electromagnet becomes zero before the electron beam completes one whole circle after passing the intersection.
The electron beam fed into the equilibrium orbit loses its kinetic energy due to the braking action of the six bending electromagnets when synchrotron orbital radiation is emitted. The radio frequency cavities are provided to compensate for this kinetic energy loss. That is, the electron beam maintains its position on the orbit by obtaining kinetic energy from an accelerating electric field produced within the radio frequency cavities.
The path for the electron beam is contained within the vacuum tank, and the inflector as well as the bump electromagnet are also usually installed within the tank. In the conventional charged particle apparatus this construction requires straight sections for installing the inflectors, the quadrupole electromagnets, the radio frequency cavities and the like, which makes it difficult to provide a sufficiently compact apparatus.